Select all the choices that have a formation enthalpy of zero. A. Oxygen gas, O2(g) B. Nitrogen gas, N2(g) C. Atomic chlorine, Cl(g) D. Magnesium metal, Mg(s) E. Carbon monoxide, CO(g)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Select all the choices that have a formation enthalpy of zero.
A. Oxygen gas, O2(g)
B. Nitrogen gas, N2(g)
C. Atomic chlorine, Cl(g)
D. Magnesium metal, Mg(s)
E. Carbon monoxide, CO(g)
standard enthalpy of formation:
The standard enthalpy of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.
According to the definition, all elements in their standard states have a standard enthalpy of formation of zero, as there is no change involved in their formation.
From the given option the elements are as follows:
A. Oxygen gas, O2(g)
B. Nitrogen gas, N2(g)
D. Magnesium metal, Mg(s)
Note: the standard state of chlorine is Cl2.
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